Inside-out heat sink

ABSTRACT

A heat sink has a fenestrated outer surface and internal structure supporting the outer surface to facilitate heat transfer from, and provide structural rigidity to, the heat sink.

FIELD OF THE INVENTION

[0001] This invention relates to heat sinks, and more particularly, to heat sinks used to cool integrated circuits.

BACKGROUND OF THE INVENTION

[0002] Heat sinks are used to regulate the amount of latent heat in a device and transfer excess heat from the device to some cooling medium.

[0003]FIG. 1 shows one example of a conventional heat sink 100, referred to herein as a “pin-type” heat sink in both isometric and orthographic projection. The heat sink 100 of FIG. 1 has a body 102 that is illustratively “L” shaped. The forward face 104 of the heat sink 100 is designed to be placed in contact with an integrated circuit (not shown) and to draw heat from the integrated circuit by conductive heat transfer. A set of pins 106 extend outward from the body and are spaced apart from each other and arranged to allow for the cooling medium to pass among the pins 106 to thereby remove heat from the pins by convective heat transfer.

[0004]FIG. 2 is another example of a conventional heat sink 200, referred to herein as a “fin-type” heat sink. The heat sink of FIG. 2 is identical to the heat sink of FIG. 1 except, instead of pins, the heat sink of FIG. 2 has a series of fins 202 extending outwardly from the body 204 in planes perpendicular to the longitudinal axis of the heat sink 200.

[0005] While both of the above heat sinks 100, 200 are useful for cooling integrated circuits, when used with integrated circuits containing active optical devices such as lasers and/or detectors and passive optical components such as fibers, lenses or modulators (among other components) they have several problems due to various factors largely unique to such devices. First, alignment among the optical components is often critical. A misalignment of even a micron can cause one or more components to be useless.

[0006] Second, the operational characteristics of active optical devices can be very heat sensitive. Temperature changes can cause the wavelength of a given laser to change because excess latent heat increases the effective cavity size of a laser.

[0007] Third, heat sinks act as a moment arm and transmit applied forces to the integrated circuit to which they are attached. This is not a problem for devices that generally remain fixed however, where such heat sinks are part of a module that will be repeatedly connected and disconnected from another item (generically referred to herein as “coupled” or “coupling”), such as a connector plug, and alignment between the module and the connector plug are critical the flexing forces transmitted by the heat sink during coupling can introduce misalignments in excess of one micron.

[0008] Fourth, the structural rigidity of the heat sinks 100, 200 of FIG. 1 and FIG. 2 are different in each of the X, Y and Z directions. In fact, the rigidity of both those heat sinks 100, 200 is lowest with respect to bending forces applied rotationally in the Y-Z plane because of the narrow thickness of parts of the body 100, 200 in that plane. This difference in directional structural rigidity means that thermal fluctuations can cause the heat sinks themselves create and transmit or apply flexing forces to the integrated circuit to which they are attached, thereby causing misalignment.

[0009] Finally, the efficiency of the heat sink is a function of the number of pins or fins, the size of the pins or fins, the heat sink body material, the pin or fin material and the pin or fin placement relative to the direction of movement of the cooling medium. However, the maximum volume the heat sink can occupy limits the extent to which each can be varied and hence the maximum efficiency.

[0010] Thus, there is a need for a heat sink that can be used with integrated circuits having components susceptible to misalignment, that reduces the likelihood of heat sink related misalignment while occupying the same overall volume as a conventional pin-type or fin-type heat sink, the “overall volume” as used herein having the definition of the volume that would be occupied by the smallest solid rectangular or cylindrical block that can contain the heat sink.

SUMMARY OF THE INVENTION

[0011] I have devised an “inside-out” heat sink that addresses the problems of conventional heat sinks, making it possible to provide a heat sink that occupies the same overall volume as a conventional pin-type or fin-type heat sink but: a) is structurally more rigid than the conventional pin-type or fin-type heat sink made of the identical material and occupying the same overall volume, and b) is a more efficient heat sink than the conventional pin-type or fin-type heat sink made of the identical material and occupying the same overall volume under identical, typical operational conditions in terms of cooling medium, direction of flow, and temperature of cooling medium.

[0012] The advantages and features described herein are a few of the many advantages and features available from representative embodiments contained herein and are presented only to assist in understanding the invention. It should be understood that they are not to be considered limitations on the invention as defined by the claims, or limitations on equivalents to the claims. For instance, some of these advantages are mutually contradictory, in that they cannot be simultaneously present in a single embodiment. Similarly, some advantages are applicable to one aspect of the invention, and inapplicable to others. Thus, this summary of features and advantages should not be considered dispositive in determining equivalence. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an example of a conventional pin-type heat sink;

[0014]FIG. 2 is an example of a conventional fin-type heat sink;

[0015]FIG. 3 is one illustrative example of an inside-out heat sink implementation according to the present invention;

[0016]FIG. 4 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0017]FIG. 5 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0018]FIG. 6 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0019]FIG. 7 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0020]FIG. 8 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0021]FIG. 9 is another illustrative example of an inside-out heat sink implementation according to the present invention;

[0022] FIGS. 10-17 are representative illustrative examples of some of the myriad of outer surfaces that can be used for creating inside-out heat sinks according to the present invention;

[0023]FIG. 18 is an example of an example application for a representative inside-out heat sink according to the present invention; and

[0024]FIG. 19 is an example module incorporating a representative inside-out heat sink according to the present invention.

DETAILED DESCRIPTION

[0025]FIG. 3 is an example of one implementation of a heat sink 300 incorporating the present invention.

[0026] As shown in FIG. 3, the body 302 of the heat sink 300 is shaped like a pair of discrete abutting rectangular boxes 304, 306 geometrically referred to as right rectangular parallelepipeds, with the surface 308 of the body 302 defining an internal volume for the body. The smaller of the two “boxes” 304 is a solid “conduction” portion and the larger of the two “boxes” 306 is a fenestrated “convection” portion.

[0027] The conduction portion 304 includes a face 310 that is suitably sized and dimensioned to be coupled to an integrated circuit (not shown), that contains precision aligned elements and generates heat when it is operating, in order to sink generated heat into the conductive portion 304 through conductive heat transfer. As shown, the conductive portion 304 has a rectangular conduction face 310 to serve that purpose. The conductive portion 304 also abuts the convective portion 306 at a common face 312 of suitable size to ensure that a desired level of heat transfer from the conductive portion 304 to the convective portion 306 will occur.

[0028] Both the conductive portion 304 and the convective portion 306 are made of heat conductive material, for example a metal such as aluminum, copper, brass, iron, zinc, etc. or an alloy.

[0029] Depending upon the particular implementation, the conductive portion 304 and the convective portion 306 can be made of a common material (preferably having a high conductivity) or of different materials. In addition, depending upon the particular implementation, the conductive portion 304 and the convective portion 306 can be physically formed simultaneously, concurrently or sequentially.

[0030] Where different materials are used for the two portions, it is desirable that both have a high conductivity. It is also highly desirable, but not mandatory, that the material used for the convective portion 306 have a lower conductivity than the conductive portion 304 if the two are made of different materials. In addition, where different materials are used, care should be taken in material selection to ensure that detrimental galvanic coupling or corrosion between the two materials does not occur.

[0031] As shown in FIG. 3, the convective portion 306 has six faces, the “common” or intermediate face 312, a top face 314, a rear face 316, a right side face 318, a left side face 320 and a bottom face 322.

[0032] As shown in FIG. 3, fenestrations 324 cover part of the outer surface 308 of the convection portion 306 of the body 302. In particular, in FIG. 3 there are fenestrations 324 on the top 314, rear 316, right 318 and left 320 faces. A set of passages 326 within the body 302 interconnect some of the fenestrations 324 to others. For example, as shown in FIG. 3, straight-through passages connect the fenestrations on the right face 318 with the fenestrations on the left face 320. In contrast, straight passages extend into the body 320 from the fenestrations on the top face 314, and from the back face 316 but they all “dead end” within the body 302 (i.e. they do not go all the way through the body 302 ). The passages are deliberately placed at particular locations and interval spacings so as to create a series of interconnections among the passages 326. As a result, any given fenestration on the surface 308 will be connected to at least one other fenestration, with most being connected to two or more other fenestrations via the interconnections.

[0033] As shown in FIG. 3, the passages extending inward from each of the fenestrations on a given face are all parallel to each other. In addition all of the passages illustratively shown in FIG. 3 interconnect at right angles. In addition, the passages extending inward from the rear face 316 all run parallel to the longitudinal axis of the body 302 of the heat sink 300.

[0034] Despite the interconnections, in this and the examples below, passage placement is organized to ensure that structure exists between the walls 328 that define particular passages so as to create multiple continuous sections that linearly span the body 302. The structure between the passage walls 328 thereby forms a structural core or lattice within the outer surface 308 of the body 302 which provides support for the outer surface 308 and structural rigidity to the body 302, as a whole, approaching that of the body 302 if it were solid—at least with respect to the typical forces encountered or applied when the heat sink is part of a module or connector and the module is in operation, or those normally encountered, when the module or connector is part of an assembly that can be repeatably coupled, during coupling.

[0035] As shown in FIG. 3, the fenestrations and passages are all circular in cross section. Depending upon the particular implementation however, as shown below in connection with other example, other cross-sectional shapes can be used, for example, ovals, triangles, squares, rectangles, etc. the particular shape being more a function of manufacturability and application than of the invention.

[0036] It should be understood however that the particular shape used for the fenestrations or passages and their placement will affect the rigidity of the body as well as its ability to efficiently function such that certain combinations will be unsuitable for particular applications and others may be reasonably considered unmanufacturable or unusable.

[0037]FIG. 4 is another illustrative example of the orthographic projection for an inside-out heat sink 400 implementation according to the present invention. The heat sink 400 of FIG. 4 is identical to the heat sink 300 of FIG. 3 except that the fenestrations 402 on the outer surface 404 and the passages interconnecting the fenestrations are square in cross section.

[0038]FIG. 5 is another illustrative example of an inside-out heat sink implementation according to the present invention. The heat sink 500 of FIG. 5 is similar to the heat sink of FIG. 4 in that the outer surface 502 of the body 504 is of identical shape and size to the heat sink of FIG. 4 and the fenestrations are all square. However, there are only two fenestrations 506 on each of the right face 508 and left face 510. In addition, the passages 516 interconnecting the fenestrations on the right face 508 to the fenestrations on the left face 510 are angled with respect to those faces so that the fenestration closest to the conduction portion 512 is connected to the fenestration on the opposite face closest to the rear face 514. As a result, the two passages 516 intersect at about the middle of the body 504. There are also fenestrations on the rear face 514, however they are smaller in size than those on the right face 508 or left face 510 so that four fit within the same area on the surface 502 of the body. Like the passages extending inward from the fenestrations on the rear face 316 of FIG. 3, the passages extending inward from the fenestrations on the rear face of FIG. 5 run parallel to each other along the longitudinal axis of the heat sink 500. However, unlike FIG. 4, the passages extending from the rear face 514 of FIG: 5 extend to different depths within the body 504 and the spacing between some of the passages and their adjacent passages differs so that the upper row 518 of passages is closer to the lower row 520 than the outermost columns 522, 524 are to the innermost columns 526, 528. In addition, the two innermost columns 526, 528 are spaced from each other by almost twice the distance as between the outermost columns 522, 524.and the innermost columns 526, 528. In addition, the fenestrations on the upper face 530 are irregularly spaced relative to each other because they are arranged for maximum intersection with the other passages within the body. Finally, as with the fenestrations of the heat sink of FIG. 3, in FIG. S passages extend through the body 504 to connect the right face fenestrations to the left face fenestrations, whereas none of the rest of the passages extend fully through the body 504 to the opposite face. As a result, a part of the body 504 remains solid beyond the intermediate face 532. This effectively extends the conduction portion 534 farther into the body 504.

[0039]FIG. 6 is another illustrative example of an inside-out heat sink implementation according to the present invention. The heat sink 600 of FIG. 6 is similar to the heat sinks of FIG. 3 and FIG. 5. Like the heat sink 300 of FIG. 3, the fenestrations and passages are all circular, and the passages extending inward from a given face are all parallel to each other.

[0040] In addition, like the heat sink 500 of FIG. 5, passages extending inward from the rear face 624 go to different depths within the body 602 so that a larger portion of the body 602 is solid and serves as the conduction portion 604.

[0041] However, unlike the heat sinks 300, 500 of FIG. 3 and FIG. 5, with the heat sink 600 of FIG. 6, only the rear-most eight fenestrations 606 on the right face 608 have associated passages that extend through the body to corresponding fenestations on the left face 610. In addition, the bottom face 612 has two rows 614, 616 of fenestrations directly below the outermost rows 618, 620 of fenestrations on the top face 622 so that parallel passages extending perpendicular to the top and bottom faces connect the outermost rows 618, 620 of fenestrations on the top face 622 to the coinciding fenestrations on the bottom face 612. Finally, unlike the heat sinks of FIG. 3, FIG. 4 and FIG. 5, the heat sink of FIG. 6 is not symmetrical with respect to a plane passing through the longitudinal axis parallel to the right face 608 or left face 610.

[0042]FIG. 7 is another illustrative example of an inside-out heat sink 700 implementation according to the present invention. Unlike the example heat sinks of FIG. 3 through FIG. 6 however, the outer surface 702 of the body 704 of the heat sink of FIG. 7 is cylindrical in shape whereas the outer surfaces of the heat sinks of FIG. 3 through FIG. 6 were made up of right parallelepipeds. In addition, there is no clear demarcation between the conduction portion 706 and the convection portion 708, although there is a clearly delineated conduction face 710 of suitable size for coupling to the integrated circuit of interest.

[0043] In the heat sink of FIG. 7, a series of columns, defined by planes perpendicular to the longitudinal axis, of eight circular fenestrations are located around the outer surface 702 of the body 704 with the fenestrations within and among the columns being equally spaced from each other. In addition, the fenestrations in each column are longitudinally aligned with each other.

[0044] Passages 712 extend radially inward from the fenestrations on the outer surface 702 at alternating depths so that the fenestrations on the X-axis interconnect as do the fenestrations on the Y-axis. However, the fenestrations between the X-axis and the Y-axis only extend partway inward.

[0045] As with the prior examples, the rear face 714 is also fenestrated. In the example of FIG. 7, the fenestrations on the rear face 714 are arranged to form a pair of concentric circles and are aligned with the inwardly extending passages from the fenestrations on the outer “cylinder portion” of the outer surface 702. A set of parallel passages extend inward from the fenestrations on the rear face 714 parallel to the longitudinal axis 716 of the heat sink 700 in order to intersect with the passages extending radially into the body 704. The passages from the fenestrations on the rear face 714 also extend to different depths with the passages from the outermost circle fenestrations extending all the way to the column closest to the conduction face 710 whereas the passages from the inner circle only extend to about the middle of the body 704. As with the prior examples, the placement of the passages creates a core or lattice within the body 704 made up of multiple continuous linear sections in different directions spanning the body 704 for structural rigidity.

[0046]FIG. 8 is another illustrative example of an inside-out heat sink 800 implementation according to the present invention. The heat sink 800 of FIG. 8 is similar to the heat sink 700 of FIG. 7 in that it is cylindrical in shape and is fenestrated on the outer surface. However, unlike the heat sink 700 of FIG. 7, the fenestrations on the heat sink 800 of FIG. 8 are arranged in quadrants 802, 804, 806, 808 of three fenestrations per quadrant 802, 804, 806, 808 in a given column on the outer surface 810. The outer surface fenestrations of FIG. 8 are, however, longitudinally aligned as with the outer surface fenestrations of FIG. 3.

[0047] Passages extend inward from the fenestrations of a given quadrant 802, 804 parallel to each other so that they connect those fenestrations with the fenestrations on the opposite quadrant 806, 808. As a result therefore, as shown in FIG. 8, all the passages connecting the fenestrations on the outer surface 810 are either parallel to the Y-axis or parallel to the X-axis leaving the material that forms the walls that provide for heat transfer and form the linear sections of the internal core or lattice.

[0048] Similar to FIG. 7, the rear face 812 of the heat sink 800 of FIG. 8 is also fenestrated however, the fenestrations are aligned along the X-axis and the Y axis instead of being placed radially about the longitudinal axis. The passages extending into the body defined by the outer surface 810 from the rear face 812 are all parallel to each other and extend to the same depth so as to intersect the passages of the column closest to the conduction face 814. As a result, any given fenestration in a particular quadrant is connected to a fenestration in every other quadrant and to a fenestration on the rear face 812.

[0049]FIG. 9 is another illustrative example of an inside-out heat sink 900 implementation according to the present invention. In the example of FIG. 9, the convection portion 902 of the body 904 is of cruciform cross section having an outer surface 906 defined by twelve faces 908 each a right rectangular polygon in shape. Each face 908 is fenestrated as described above with passages interconnecting various fenestrations and intersecting each other at right angles. The passages within each of the “arms” of this heat sink 900 interconnect fenestrations on opposite parallel faces to each other. In addition, the front faces 910 of the “arms” are also fenestrated and passages extending into the body 904 from the rear face 912 of the body at the “arms” interconnect the fenestartions on the arms of the rear face 912 to the fenestrations on the opposite parallel fenestrations on the front faces 910 of the arms. As shown, the rear face 912 also has a central fenestration 914 concentric with the central longitudinal axis of the heat sink 900. However, the passage extending inward from the central fenestration 914 on the rear face 912 that only extends far enough into the body 904 to intersect the passages closest to the conduction portion 916.

[0050] Having illustrated a number of examples of inside out heat sinks implementing the invention, it should be appreciated that numerous other configurations are possible. For example, in addition to varying the material(s) used, the size and/or shape of the fenestrations, the cross sectional shape of the passages and/or their orientation (whether relative to some plane or axis or each other), different outer surface shapes can also be used.

[0051]FIGS. 10 through 17 are representative illustrative examples of the myriad of outer surface shapes that can be used for creating inside-out heat sinks according to the present invention. In each of FIGS. 10 through 17 the fenestrations and passages are not shown so that the outer surface shapes can be more clearly understood without clutter. Advantageously, use of the invention provides the ability to vary the shape of the outer surface so that the amount of cooling medium that can enter the body from multiple directions can be maximized for the application.

[0052]FIG. 10 is an example of an outer surface 1000 shaped like a representative frustum of a pyramid. In this example, cross sections of the pyramid parallel to its base are squares of differing sizes. Of course, for particular applications, a heat sink using this shape could use any one of the faces as the conduction portion. In addition, all the faces need not be equally fenestrated and, as illustrated above, some may not be fenestrated at all.

[0053]FIG. 11 is an example of an outer surface 1100 shaped like another representative frustum of a pyramid. In this example, cross sections of the pyramid parallel to its base are pentagons of differing sizes. As with FIG. 10, for particular applications, a heat sink using this shape could use any one of the faces as the conduction portion. In addition, as with all the heat sinks incorporating the invention, all the faces need not be equally fenestrated and, as illustrated above, some may not be fenestrated at all.

[0054]FIG. 12 is an example of another outer surface 1200. In the example of FIG. 12, the conduction portion 1202 is disc shaped and the convention portion 1204 has a triangular cross section of uniform size along the longitudinal axis.

[0055]FIG. 13 is another example of a polyhedral outer surface 1300 shape made up of two parallel facing equally sized octagons 1302, 1304 connected by eight rectangular faces 1306 (some of which are obscured from view).

[0056]FIG. 14 is another example of a polyhedral outer surface 1400 shape made up of parallel facing hexagons 1402, 1404. In the example of FIG. 14 however, the conduction portion 1406 is of uniform cross section whereas the convection portion 1408 is of increasing cross sectional area as the distance from the conduction portion 1406 increases in a longitudinal direction.

[0057]FIG. 15 is another example of a polyhedral outer surface 1500 shape made up of two parallel facing equally sized seven sided polygons. As shown, there is a clear delineation 1502 between the conduction portion 1504 and the convection portion 1506. This is intended to illustrate and remind the reader that, although of uniform cross section, the heat sinks described herein can be, and in this example it is, made up of different materials.

[0058] The above examples have illustrated outer surfaces where the two ends are of a common shape. It should be understood however that, for some implementations of the invention, this need not necessarily be the case. For example, FIG. 16 shows an example polyhedral outer surface 1600 where one end 1602 is square in shape and the end 1604 facing the square and 1602 is octagonal in shape, and the two are connected by faces that are alternatingly rectangular and triangular in shape. Similarly, in the outer surface 1700 example of FIG. 17, one end 1702 is rectangular in shape and the other end 1704 is oval. The two are connected by four planar triangles (only three of which are shown) each sharing a common side with the square end 1702, and a set of four curved triangular surfaces 1708 (only two of which are visible).

[0059] Thus, it should now be understood that by combining different shapes a myriad of different outer surfaces can be obtained. As a result, we collectively refer to outer surfaces that are not square or rectangularly “box” shaped, or uniformly cylindrical (i.e. they are cone shaped or made up of polygons where at least one face is of a shape other than a rectangle or square) as being an “N-hedron” or “N-hedron” in shape for simplicity.

[0060] Having described a number of different inside-out heat sink structures, the function and operation of such heat sinks will now be described, for simplicity with reference to example structures shown in simplified manner in FIG. 18 and FIG. 19.

[0061] With reference to FIG. 18, the example inside-out heat sink 1800 is coupled to an integrated circuit 1802, for example, a circuit chip containing active optical devices 1804 as lasers and/or detectors hybridized to an electronic chip 1806. The electronic chip 1806 contains, for example, the drive, and possibly also control, circuitry for those optical devices 1804. This hybridized unit is, in turn, connected to a circuit board 1808 (and possibly other components) shown for purposes of simplicity as a “ghost” box.

[0062] Depending upon the particular application, the coupling of the heat sink 1800 to the integrated circuit 1802 will either be a direct physical connection, with the two being in actual physical contact, or it will be indirect, with the two having some conductive medium or media, such as a thermal cream(s) and/or thermal expansion interface matching materials, in between.

[0063]FIG. 19 is a more detailed side view of an example inside-out heat sink 1900 such as shown in FIG. 3 used in conjunction with an example module 1902. The module 1902 contains a hybridized unit 1904 (made up of at least a group of active optical devices 1906 and an electronic chip 1908 that drives and controls the active optical devices). The active optical devices 1906 are precisely placed so as to be aligned with devices and/or fiber bearing element(s) to which the module 1902 can be coupled. The hybridized unit 1904 is, in turn, connected to a circuit board 1910 via, for example, a ball grid array 1912, leads or pins. The module 1902 may also have other connection points 1914 through which the module 1902 can be connected to other devices or elements not relevant to the invention.

[0064] The module 1902 is placed so that the heat sink 1900 is exposed to a flow of a cooling medium external to the heat sink 1902. In the example of FIG. 19, the cooling medium is air, although with straightforward modification to protect the optical and/or electronic components, it should be understood that other cooling media, including various gasses or liquids could be used.

[0065] The fenestrations allow the cooling medium to flow, in a number of directions, from external 1916 to the heat sink body into the heat sink body 1918. The cooling medium then flows through the internal passages until exiting the body 1918. During device operation, heat is conducted away from the unit 1904 (through conductive heat transfer) by the conduction portion and internal body material lattice (i.e. core of the heat sink). As the cooling medium passes through the body interior, heat will be transferred to the fluid (by convective heat transfer) via the walls of the passages. The fluid then exits the body via other fenestrations. Depending upon the orientation of the heat sink and the direction(s) of fluid flow, the specific amount of cooling will vary however, in most cases, the cooling will be significantly better than a pin-type or pin-type heat sink of the same overall volume and material under internal conditions.

[0066] Notably, for a given overall volume, inside-out heat sinks constructed according to the invention can have significantly better cooling ability under identical environmental conditions than non-fenestrated pin-type or non-fenestrated fin-type heat sinks of identical material and overall volume. One example of the significance of the invention is illustrated with reference to Table 1. Table 1 compares the cooling ability of a non-fenestrated pin-type heat sink similar to that of FIG. 1 with an inside-out heat sink similar to that of FIG. 3 having the same overall volume and made of the same material under the same environmental conditions. TABLE 1 DELTA TEMPERATURE (chip temp. to ambient in degrees Celsius) Air Flow Direction Side Top Rear Side/Rear Velocity 200 200 200 200 LFM Pin-type Heat Sink 25.1 10.3 29.1 25.1 (1.4 Watt) Inside-Out Heat Sink 14.6 7.3 16.5 18.1 (1.4 Watt) % Improvement 41.8 29.1 43.3 27.9

[0067] As shown in Table 1, use of an inside-out heat sink improves the cooling ability by at least 27% and by as much as 43+% depending upon the particular direction of fluid flow, in this case air, at a fluid flow rate of 200 linear feet per minute (LFM). In addition, the inside-out heat sink was at least as rigid in each of the x, y and z directions, and in the y direction more rigid, than the pin-type heat sink to which it was compared.

[0068] I knew that, when the integrated circuit to which it was connected was operating, the pin-type heat sink of Table 1 was quite hot to the touch. Remarkably, the inside-out heat sink was actually cool to the touch under the same operating conditions. The degree of difference was significant and well beyond what I expected under the circumstances.

[0069] Table 2 shows a comparison, obtained through simulation, of the cooling ability of other pin-type heat sinks as compared with fenestrated heat sinks configured according to the present invention used in conjunction with larger integrated circuits generating the power shown below. In Table 2, the type#1 heat sink is a larger version of the heat sink of FIG. 3. The pin-type heat sink to which it is compared is similar to the heat sink of FIG. 1 but has the same overall volume as the type#1 heat sink for comparison. The type#2 heat sink is the heat sink of FIG. 6. The pin-type heat sink to which it is compared is similar to the heat sink of FIG. 1 but has the same overall volume as the type#2 heat sink for comparison. TABLE 2 DELTA TEMPERATURE (chip Type temp. to ambient in degrees Celsius) Air Flow Direction Side Velocity LFM 200 Pin-type Heat Sink (2.2 27.6 Watt) #1 Inside-Out Heat Sink (2.2 17.3 Watt) % Improvement 37.3 Pin-type Heat Sink (6.4 50.3 Watt) #2 Inside-Out Heat Sink (6.4 33.4 Watt) % Improvement 33.6

[0070] Notably, both the type#1 and type#2 heat sinks show more than a 30% improvement in cooling when the air flow is purely from the side. Based upon Table 1 and Table 2, I expect that analogous results in Table 2 would be achieved for the other directions from Table 1.

[0071] Having now described the invention by way of a number of example implementations and an example operation, it should be appreciated that many different variants can be created. For example, as noted above, the heat sink can be made of any heat conductive material. In addition, the fenestrations can be virtually any geometric shape. Similarly, the passages can be of virtually any manufacturable cross sectional shape. In addition, the passages and/or the fenestrations can be flared where they join, for example to provide a smoother flow path for the fluid used as the cooling medium. The cross sectional shape of a given passage and the fenestration(s) to which it connects can be of different shapes with a shape transition area in-between. Multiple fenestration shapes can be used on a single heat sink. Multiple passage shapes can be used within a single heat sink. The heat sink body can be formed by any method usable for forming the intended material into the desired shape including, for example, one or more of the following alone or in combination: molding, casting, sintering, laminating, electro-depositing, forging, rolling, milling, turning, to name a few. Similarly, the fenestrations can be formed as part of the process, or thereafter through, for example drilling, milling, other machining processes, etc. Finally, bodies of one type can be formed from bodies of other types. For example, a heat sink such as shown in FIG. 3 can be made into a heat sink similar to the one of FIG. 8 by, for example, taking the heat sink of FIG. 3 and turning it in a lathe, or rounding it over using a milling or grinding process, assuming of course proper fenestration and passage placement.

[0072] Thus, while we have shown and described various examples employing the invention, it should be understood that the above description is only representative of illustrative embodiments. For the convenience of the reader, the above description has focused on a representative sample of all possible embodiments, a sample that teaches the principles of the invention. The description has not attempted to exhaustively enumerate all possible variations given the myriad of different possibilities that can be achieved merely from using different permutations or combinations of those features described, let alone variations involving equivalents to those features. That alternate embodiments may not have been presented for a specific portion of the invention, or that further undescribed alternate embodiments or other combinations of described portions may be available, is not to be considered a disclaimer of those alternate embodiments. It should be understood that many of those undescribed embodiments are within the literal scope of the following claims, and others are equivalent. 

What is claimed is:
 1. An inside-out heat sink comprising: a body having at least three faces, the at least three faces defining an outer surface of the body and a volume within the outer surface, the body comprising a heat conductive material, at least one of the faces being configured to be coupled to an integrated circuit containing optical chips and electronic circuitry which, when operating, acts as a heat source, the at least one of the faces being further configured to receive heat from the heat source by conductive heat transfer, a set of walls enclosed within the body and defining multiple inter-linked passages, each of the passages extending from at least one of the faces into the volume, at least some of the passages being oriented differently with respect to others of the passages, and wherein at least a few of the passages extend from one of the faces to another of the faces, the passages being arranged relative to each other so as to permit entry of a cooling medium into several of the passages from multiple directions external to the body, allow the cooling medium to flow through the passages to facilitate convective heat transfer between the walls and the fluid, and allow the cooling medium to exit to external to the body, and the set of walls further defining multiple continuous sections linearly extending from each of the at least three faces to each of the other of the at least three faces.
 2. The heat sink of claim 1 wherein at least some of the walls are located so as to be equal in extent to a linear cross section of the body taken through each of the at least some walls in the plane of the wall, and wherein the at least some of the walls form a lattice within the body that provides structural rigidity to the body while allowing for convective heat transfer between the core and the fluid when the fluid is passing through a set of the passages.
 3. A heat sink comprising: a heat conductive core comprising a specified material and having a series of interconnecting internal passages that provide a multi-directional pathway for a fluid from an exterior surface of the core into the core, through the core, and external to the core; the heat conductive core forming a structural lattice within the heat sink to provide rigidity to the heat sink; a portion of the heat conductive core being sized for coupling to an integrated circuit heat source to conduct heat generated by the integrated circuit heat source into the core for dissipation through convective heat transfer to the fluid when it is passing through the interconnecting internal passages; and the heat sink apparatus occupying an overall volume such that it has both a lower mass and greater heat transfer ability than either a pin-type heat sink or a fin-type heat sink made of the specified material that occupies the overall volume under identical environmental conditions of generated heat, fluid type and fluid flow.
 4. A cooling device comprising: an outer surface, wherein the outer surface is fenestrated to allow for passage into the device, from multiple directions, of a cooling fluid from external to the device through some of the fenestrations and to allow for passage out of the device of the cooling fluid from internal to the device; a core within the device, and bounded by the outer surface, to provide structural support and flexural rigidity to the outer surface, the core comprising a predetermined heat conductive material and having a conductive heat transfer surface configured to sink heat generated by a circuit module, having aligned optical components therein, into the core when the circuit module is coupled to the conductive heat transfer surface and is operational; a set of passages within the core and interconnecting at least some of the fenestrations to other of the fenestrations, the passages having walls defining convective heat transfer surfaces of sufficient dimensions to allow for transfer of heat from the core to the cooling fluid by convection when the cooling fluid passes through at least some of the passages of the set of passages; the cooling device occupying an overall volume such that the cooling device is more rigid, has a lower mass, and a greater heat transfer ability than either a non-fenestrated pin-type heat sink or a non-fenestrated fin-type heat sink made of the predetermined material and occupying the overall volume under identical environmental conditions.
 5. The device according to claim 4 wherein the predetermined material comprises a metal.
 6. The device according to claim 5 wherein the metal comprises at least one of aluminum, copper, iron, steel, brass, nickel, silver, or gold.
 7. The device according to claim 5 wherein the predetermined material comprises an alloy.
 8. The device according to claim 5 wherein the outer surface defines a parallelepiped.
 9. The device of claim 8 wherein the parallelepiped is a right paralellepiped.
 10. The device according to claim 9 wherein the outer surface defines a cuboid.
 11. The device according to claim 5 wherein the outer surface defines a cylinder.
 12. The device according to claim 5 wherein the outer surface defines a pyramidal frustum.
 13. The device according to claim 5 wherein the outer surface defines an N-hedron.
 14. The device according to claim 5 wherein the outer surface defines a prism.
 15. The device according to claim 5 wherein the outer surface defines a cruciate shape.
 16. The device according to claim 5 wherein the outer surface comprises at least four sides and wherein there are at least three fenestrations on each of the at least four sides.
 17. The device according to claim 5 wherein passages in the set of passages are parallel to each other.
 18. The device according to claim 5 wherein particular passages in the set of passages. are at an angle to each other.
 19. The device according to claim 18 wherein the angle is a right angle.
 20. The device according to claim 18 wherein a first of the passages, a second of the passages and a third of the passages are all at right angles to each other.
 21. The device according to claim 5 wherein the surface defines a longitudinal axis and a designated set of passages have an equal spacing with respect to the longitudinal axis.
 22. The device according to claim 18 wherein the designated set of passages radially extend between the longitudinal axis and a designated set of fenestrations. 